© NASA/Ricardo Nunes

Venus at dichotomy

Dominic Ford, Editor
From the Inner Planets feed

Objects: Venus
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Venus will reach half phase in its 2018 evening apparition. It will be shining brightly at mag -4.3.

From Ashburn , this apparition will not be one of the most prominent but prominent, reaching a peak altitude of 27° above the horizon at sunset on 13 Jun 2018.

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2018 evening apparition of Venus

09 Jan 2018 – Venus at superior solar conjunction
13 Jun 2018 – Venus at highest altitude in evening sky
15 Aug 2018 – Venus at dichotomy
17 Aug 2018 – Venus at greatest elongation east
25 Sep 2018 – Venus at greatest brightness

The table below lists the altitude of Venus at sunset over the course of the apparition. All times are given in Ashburn local time.

Date Sun
sets at
sets at
at sunset
at sunset
Mag Phase
15 Mar 201819:1820:2813°west-3.996%
25 Mar 201819:2720:5215°west-3.995%
04 Apr 201819:3921:1617°west-3.994%
14 Apr 201819:4821:3920°west-3.992%
24 Apr 201819:5722:0322°west-3.990%
04 May 201820:0722:2424°west-3.988%
14 May 201820:1822:4325°west-4.085%
24 May 201820:2622:5826°west-4.083%
03 Jun 201820:3123:0727°west-4.080%
13 Jun 201820:3623:0827°west-4.076%
23 Jun 201820:4223:0927°west-4.073%
03 Jul 201820:3922:5926°west-4.169%
13 Jul 201820:3622:4925°west-4.165%
23 Jul 201820:3222:3423°west-4.261%
02 Aug 201820:2322:1421°west-4.256%
12 Aug 201820:1021:5820°west-4.352%
22 Aug 201819:5921:3417°south-west-4.446%
01 Sep 201819:4321:1415°south-west-4.440%

Altitude of Venus at sunset

A graph of the phase of Venus is available here.

Apparitions of Venus

26 Oct 2015 – Morning apparition
12 Jan 2017 – Evening apparition
03 Jun 2017 – Morning apparition
17 Aug 2018 – Evening apparition
06 Jan 2019 – Morning apparition
24 Mar 2020 – Evening apparition
13 Aug 2020 – Morning apparition

Observing Venus

Venus's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is lost in the Sun's glare much of the time.

It is observable for a few months each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions repeat roughly once every 1.6 years.

On these occasions, Venus is so bright and conspicuous that it becomes the third brightest object in the sky after the Sun and Moon. It is often called the morning star or the evening star.

Venus's phase

Venus's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon.

Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times.

Venus shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few days, only because Venus's orbit is not quite perfectly aligned with the ecliptic.

Venus's position

The coordinates of Venus when it reaches dichotomy will be:

Object Right Ascension Declination Constellation Angular Size
Venus 12h27m10s -04°20' Virgo 23.7"
Sun 09h37m +14°08' Leo 31'34"

The coordinates above are given in J2000.0.

The sky on 15 August 2018
Twilight ends
Twilight begins

4-day old moon
Waxing Crescent


4 days old

Rise Culm. Set
Mercury 05:40 12:28 19:16
Venus 10:13 16:02 21:51
Moon 11:04 17:09 23:02
Mars 19:16 23:44 04:12
Jupiter 13:14 18:25 23:37
Saturn 17:02 21:47 02:31
All times shown in EDT.


The circumstances of this event were computed using the DE430 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).

This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.

Related news

15 Aug 2018  –  Venus at dichotomy
17 Aug 2018  –  Venus at greatest elongation east
05 Sep 2018  –  Venus at aphelion
25 Sep 2018  –  Venus at greatest brightness

Image credit

© NASA/Ricardo Nunes






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